From the viewpoint of protecting natural environments, researches are vigorously conducted on aliphatic polyesters that can biologically decompose in the natural environment. Among these, a poly(3-hydroxyalkanoate) (hereinafter also called P3HA) resin is known as a polymer produced by microorganisms and is attracting attention because of having excellent biodegradability. In recent years, the resin is desired to be used for a long term as, not only simply having biodegradability, a carbon fixation material that reduces carbon dioxide in the atmosphere. However, it is pointed out that because P3HA has a low crystallization rate, it takes time to solidify P3HA from the molten state during a molding process, which decreases productivity.
As a method for resolving such a problem, a method of adding a crystal nucleating agent is known, for example. The crystal nucleating agent is a primary crystal nucleus of a crystalline polymer to promote crystal growth, and therefore functions to make a crystal size finer and increase a crystallization rate.
Disclosed crystal nucleating agents for P3HA include inorganic particles such as talc, boron nitride, and calcium carbonate (Patent Document 1), sugar alcohol compounds of a specific formula (Patent Document 2), amino acids of a specific formula (Patent Document 3), amide compounds of a specific formula (Patent Document 4), and organic phosphonic acids or organic phosphinic acids, or esters or metal salts thereof, or derivatives thereof (Patent Document 5). It is also known that a zinc salt of phenylphosphonic acid of a specific formula is effective (Non-Patent Document 1).
Although these methods can increase a crystallization rate and increase crystallinity, development of a more effective crystal nucleating agent has been recently desired in order to achieve higher moldability and thermal resistance.